1. Field of the Invention
The present invention relates to a photosensitive composition, and more specifically, relates to a high sensitive photosensitive composition useful for forming colored filter segments such as red-, green-, blue-, yellow-, orange-, cyan- and magenta-colored filter segments and black matrices in a color filter which is used for a liquid crystal display device and a solid imaging element. Further, the present invention relates to a color filter formed using the photosensitive composition.
2. Description of the Related Art
A color filter includes fine stripe filter segments having two or more different hues arranged in parallel to or intersected with each other on the surface of a transparent substrate such as glass, or fine stripe filter segments horizontally and vertically arranged at a constant sequence. The filter segments are fine and the width is several microns to several hundred microns, and they are regularly arranged at a predetermined sequence by every hue.
In general, a transparent electrode for driving liquid crystal is formed on the color filter by vapor deposition or spattering in a color liquid crystal display device. Further, an alignment film for aligning the liquid crystal in a predetermined direction is formed over the transparent electrode. In order to make the best use of the performances of these transparent electrode and alignment film, the formation of them is required to be carried out at a high temperature of usually 200° C. or more, and preferably 230° C. or more.
Accordingly, the manufacture of the color filter is mainly performed at present by a method called a pigment dispersion method wherein a pigment, which is excellent in light resistance and heat resistance, are employed as a colorant.
According to the pigment dispersion method, a photosensitive colored composition (pigment resist), which disperses a pigment in a photosensitive transparent resin solution, is coated on a transparent substrate such as glass, and the solvent is removed by drying. Then the pattern exposure was conducted, and the unexposed portions are removed in a development step to form a pattern of the first color (first filter segments). Subsequently, a processing such as a heat treatment is applied to the first filter segments, if required. Thereafter, the same procedures as those described above are repeated successively for all of the remaining filter colors. In this way, a desired color filter is produced.
High sensitivity, good solubility of the non-image portions in a developing liquid and high chemical resistance of the image portions are important characteristics required in the formation of the filter segments using a photosensitive colored composition containing pigments. Requests for a color filter with higher color density and black matrices with high optical density (OD value) have been recently enhanced, and the concentration of a colorant in a photosensitive colored composition tends to be increased. However, when the concentration of a colorant is increased, other characteristics are affected. For example, the exposed portions are not sufficiently cured because of increase in the light absorption of a colorant itself. Thus, the increase of the colorant concentration is in a trade-off relationship with the maintenance of various characteristics such as sensitivity of a photosensitive composition.
A photopolymerizable composition which uses a specific binder resin in order to enhance the sensitivity and the solubility in a developing liquid is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2002-14468. This composition is high sensitive and superior in the solubility in a developing liquid. However, the binder resin is obtained by adding an epoxy compound having an ethylenically unsaturated double bond to a polymer having a carboxyl group to form hydroxyl groups by this addition reaction. The formed hydroxyl groups are subjected to an addition reaction with an isocyanate compound having an ethylenically unsaturated double bond, thus forming the binder resin.
It is necessary for a photosensitive transparent resin to be designed such that the photosensitive transparent resin satisfies many characteristics such as stability, solubility and chemical resistance by adjusting the kind and ratio of monomers. Accordingly, there is an upper limit for the ratio of monomers which can introduce an ethylenically unsaturated double bond, and it is important for coexistence of sensitivity and other characteristics at how low monomer ratio many ethylenically unsaturated double bonds are introduced.